purge: get lockbox mountpoint and unmount it
purge: get lockbox mountpoint and unmount it

Prior command was avoiding the lockbox mountpoint and the playbook was
failing with:

rmtree failed: [Errno 30] Read-only file system:
'/var/lib/ceph/osd-lockbox/4e9d8052-87c2-4fde-a56c-b8c108a3eefc/key-management-mode'

Signed-off-by: Sébastien Han <62d754cc350e84d3b1c32ae79f976f5348e74a40@redhat.com>

bengland2/ceph-ansible,jtaleric/ceph-ansible,travmi/ceph-ansible,fgal/ceph-ansible,ceph/ceph-ansible,bengland2/ceph-ansible,fgal/ceph-ansible,travmi/ceph-ansible,ceph/ceph-ansible,jtaleric/ceph-ansible,font/ceph-ansible,font/ceph-ansible